The field of the invention is controlling the amount of carbon dioxide (CO.sub.2) in the atmosphere. This may have a significant effect on global climate change, including global warming.
The carbon dioxide content of the atmosphere has been increasing. This is based on measurements over the last 40 years or more. There is concern that this increase may result in global climate change, which over time may have an adverse effect on weather, sea level and human survival.
This concern has lead to the 1992 Rio Treaty and the Kyoto Protocol of 1997. These call for significant decrease in the amount of carbon dioxide released to the atmosphere from the burning of fossil fuels by the industrial world. If these reductions are put into effect, then serious adverse consequences are expected. The economy of the industrialized world could be significantly, adversely affected. This could result in a loss of jobs, decreases in the standard of living, reduction in life span and possible political unrest. Moreover, this would not be a solution because it does not permit or require a reversal of the currently increasing levels of carbon dioxide in the atmosphere.
Carbon dioxide is released into the atmosphere both by the burning of fossil fuels, and by the recycling of plant materials. Carbon dioxide is removed from the atmosphere by the photosynthesis of plants on land and in the oceans. This removal of carbon dioxide from the atmosphere may be referred to as a carbon dioxide sink. It is the net flow (releases minus sinks) that has caused the increase in atmospheric carbon dioxide level which is of present concern. Without human intervention, the net flow of carbon dioxide into and out of the atmosphere is roughly zero, with the sources and sinks in rough balance. When fossil fuels are burned, only about 60 percent of the released carbon dioxide is subsequently taken out of the atmosphere by natural sinks. The remaining about 40 percent increases the carbon dioxide level of the atmosphere, leading to concern over climate changes.
The net carbon dioxide released into the atmosphere can be reduced, but not eliminated, by increasing the efficiency of power-producing equipment and by harnessing wind and solar power. Generally speaking, these approaches are costly and may be reaching their practical limits. We have been increasing the efficiency of heat engines for over 200 years, and may be approaching the limits of basic thermodynamics. It is very costly to harness low intensity power sources such as wind, waves, sunlight and ocean thermal gradients, especially where energy requirements are large. Moreover, these approaches can only reduce the increase in carbon dioxide concentration, never eliminate the increase. Therefore, these approaches cannot adequately address the concern over the increasing carbon dioxide content of the atmosphere.
The technology of carbon dioxide sink enhancement is in its infancy. The sequestering of carbon dioxide in geological formations is both beneficial and inexpensive, if the carbon dioxide is relatively concentrated. An example of relatively concentrated carbon dioxide is the off-gas after removal of methane from natural gas containing carbon dioxide. However, there is relatively little carbon dioxide available in such concentrated form. Most carbon dioxide is available in concentrations of from about 10 percent to about 25 percent in exhaust gases from the combustion of fossil fuels. It is quite expensive to increase the concentration of carbon dioxide from about 10 or 25 percent to about 100 percent. The preferable course of action appears to be the use of sunlight and plants to do the concentrating, and subsequently to sequester the resulting plant material in some manner.
One approach would be to plant trees. However, there is not enough land to plant sufficient trees to zero out the net carbon dioxide production. Even if there were enough land, we would have to find a place to store the resulting wood after about 50 to about 100 years, such that the wood would not rot and release carbon dioxide to the atmosphere. Thus, this approach would not sequester carbon dioxide for a relatively long period of time.
The best place to enhance plant growth is in the oceans. Ninety-eight percent of the surface of the ocean is a barren desert with almost no plant life. About sixty percent of the plant life (phytoplankton) in the oceans of the world arises from about only two percent of the surface of the oceans. A reduction in the net flow of carbon dioxide may be achieved, if some of that ninety-eight percent of the surface of the ocean is made as productive as that two percent.